Coronary hemodynamics in endothelial NO synthase knockout mice.
For the specific analysis of endothelial NO synthase (eNOS) function in the coronary vasculature, we generated a mouse homozygous for a defective eNOS gene (eNOS-/-). Western blot as well as immunohistochemical staining revealed the absence of eNOS protein in eNOS-/- mice. Aortic endothelial cells derived from eNOS-/- mice displayed only background levels of NOx formation compared with wild-type (WT) cells (88 versus 1990 pmol NOx x h-1/mg protein-1). eNOS-/- mice were hypertensive (mean arterial pressure, 135 +/- 15 versus 107 +/- 8 mm Hg in WT) without the development of cardiac hypertrophy. Coronary hemodynamics, analyzed in Langendorff-perfused hearts, showed no differences either in basal coronary flow or in maximal and repayment flow of reactive hyperemia. Acute NOS inhibition with Nomega-nitro-L-arginine methyl ester (L-NAME) in WT hearts substantially reduced basal flow and reactive hyperemia. The coronary response to acetylcholine (ACh) (500 nmol/L) was biphasic: An initial vasoconstriction (flow, -35%) in WT hearts was followed by sustained vasodilation (+190%). L-NAME significantly reduced vasodilation in WT hearts (+125%) but did not alter the initial vasoconstriction. In eNOS-/- hearts, the initial vasoconstriction was augmented (-70%), whereas the ACh-induced vasodilation was not affected. Inhibition of cyclooxygenase with diclofenac converted the ACh-induced vasodilation into vasoconstriction (-49% decrease of basal flow). This effect was even more pronounced in eNOS-/- hearts (-71%). Our results demonstrate that (1) acute inhibition of eNOS reveals a role for NO in setting the basal coronary vascular tone as well as participation in reactive hyperemia and the response to ACh; (2) chronic inhibition of NO formation in eNOS-/- mutant mice induces no changes in basal coronary flow and reactive hyperemia, suggesting the activation of important compensatory mechanisms; and (3) prostaglandins are the main mediators of the ACh-induced vasodilation in both WT and eNOS-/- mice.
Gödecke
A
A
Institut für Herz- und Kreislaufphysiologie, Heinrich-Heine-Universität, Düsseldorf, Germany. axel@herzkreis.uni-duesseldorf.de
Decking
U K
UK
Ding
Z
Z
Hirchenhain
J
J
Bidmon
H J
HJ
Gödecke
S
S
Schrader
J
J
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D003326:Coronary Circulation / Q000502:physiology*; D004730:Endothelium, Vascular / Q000201:enzymology*; D018390:Gene Targeting; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics* / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000235:genetics*
D019001:Nitric Oxide Synthase